The present invention relates to a magnetic recording and reproducing apparatus such as a video tape recorder, etc.
FIGS. 1, 2 and 3 show one example of a known magnetic recording and reproducing apparatus into which a large cassette 48 and a small cassette 25 shown by the two-dot chain lines can be selectively loaded. In the known apparatus, an apparatus housing 1 is provided with a cassette holder 2 for inserting the large cassette 48 or the small cassette 25 thereinto. The cassette holder 2 is coupled with the apparatus housing 1 by a link 3 so as to be displaced upwardly and downwardly such that the cassette inserted into the cassette holder 2 is loaded into a predetermined position in the apparatus housing 1. A first reel base 4 and a second reel base 5 are provided on the apparatus housing 1 so as to be engaged with a supply reel and a take-up reel of the large cassette 48, respectively. Furthermore, a third reel base 6 is disposed between the first and second reel bases 4 and 5 so as to be lifted and lowered vertically. At a lifted position of the third reel base 6, the first and third reel bases 4 and 6 are engageable with a supply reel and a take-up reel of the small cassette 25, respectively.
Meanwhile, as shown in FIGS. 2 and 3, a pair of microswitches 7a and 7b are, respectively, provided at opposite end portions in the cassette holder 2 and in the vicinity of a front edge of a front opening of the cassette holder 2. When the large cassette 48 has been inserted into the cassette holder 2, the large cassette 48 is brought into contact with the microswitches 7a and 7b so as to turn on the microswitches 7a and 7b such that the third reel base 6 is lowered. Hence, when the cassette holder 2 is lowered after the large cassette 48 has been completely inserted into the cassette holder 2, the supply reel and the take-up reel of the large cassette 48 are, respectively, brought into engagement with the first and second reel bases 4 and 5. On the other hand, when the small cassette 25 has been inserted into the cassette holder 2, the small cassette 25 is brought into contact with only the microswitch 7a so as to turn on the microswitch 7a. Therefore, the third reel base 6 is lifted when the third reel base 6 is disposed at a lowered position. On the other hand, if the third reel base 6 is disposed at the lifted position, the third reel base 6 is held at the lifted position. Therefore, when the cassette holder 2 is lowered after the small cassette 25 has been completely inserted into the cassette holder 2, the supply reel and the take-up reel of the small cassette 25 are, respectively, brought into engagement with the first and third reel bases 4 and 6. As described above, the small cassette 25 and the large cassette 48 can be selectively loaded into the known apparatus.
However, the known apparatus of the above described arrangement has a drawback that if the third reel base 6 has not yet been lowered completely during descent of the cassette holder 2 having a large cassette 48 inserted thereinto when the large cassette 48 is loaded into the apparatus housing 1, the large cassette 48 collides with the third reel base 6. Furthermore, the known apparatus has been disadvantageous in that if the small cassette 25 has not yet been lowered completely during descent of the cassette holder 2 having the small cassette 25 inserted thereinto when the small cassette 25 is loaded into the apparatus housing 1, the take-up reel of the small cassette 25 and the third reel base 6 may have a head-on collision so as to apply an axial contact pressure to each other with the result that descent of the small cassette 25 and ascent of the third reel base 6 cannot be performed.
Meanwhile, a rotary drive unit for driving the third reel base 6 has been earlier proposed in Japanese Patent Application No. 279549/1987 by the assignee of the present application. FIGS. 4 and 5 show this prior art rotary drive unit. In FIG. 4, a roller 11 is coupled with a motor (not shown). An idler roller 13 is urged by a spring 17 so as to be brought into pressing contact with the roller 11 and the third reel base 6. A pinatable lever 14 is so provided as to be pivoted about a shaft 15. The idler roller 13 is rotatably mounted on a shaft 16 secured to the rotary lever 14. A solenoid 18 is engaged with the rotary lever 14 by a pin 19.
In the prior art rotary drive unit of the above described arrangement, when the roller 11 is rotated by the motor (not shown), the idler roller 13 is rotated through contact of the idler roller 13 pressing against the roller 11 and the third reel base 6 by a frictional force therebetween. Furthermore, rotation of the idler roller 13 is transmitted to the third reel base 6 by a frictional force therebetween. When the solenoid 18 is energized, the rotary lever 14 is rotated about the shaft 15 in the counterclockwise direction. As a result, the idler roller 13 is spaced away from the roller 11 and the third reel base 6 such that rotation of the roller 11 is not transmitted to the third reel base 6. The above described arrangement can be used for an apparatus employing several kinds of cassettes of different sizes, in which a reel base is lifted and lowered so as to be rotated by an external motor only when the reel base is disposed at a lifted position.
However, in the prior art rotary drive unit, since the idler roller 13 acting as a frictional power transmission mechanism is used as a power transmission means, slip is produced during power transmission, so that power transmission is not performed positively. Moreover, since the frictional force changes according to environmental conditions or time, power transmission is not reliable. Furthermore, since a large contact pressure is required for pressing the idler roller 13 against the roller 11 and the third reel base 6, a large radial force is applied to shafts of the roller 11 and the third reel base 6 and thus, the roller 11 and the third reel base 6 cannot be rotated smoothly. Moreover, since the idler roller 13 is required to be properly pressed against the roller 11 and the third reel base 6, the position and size of the idler roller 13 are restricted. Even if a gear is employed in place of the idler roller 13, a problem arises that proper engagement of gears is not effected due to contact between the tooth edges and thus, it becomes difficult to operate the prior art rotary drive unit positively.